Currently, surgical procedures for cervical, lumbar, etc. spine fixation, correction, stabilization, etc. involve attaching and fixating a rod to a spine fixation device secured to a vertebral body. An appropriate rod is arranged at a predetermined position along the spine according to a known technique.
Different known spine fixation devices can be used depending on the patient's spinal disease or the type of surgery. One known spine fixation device includes a retaining head configured to hold a rod and a bone screw that screws into a vertebra as one unit. The known spine fixation device has features that can prevent relative rotation between the retaining head and the bone screw. The retaining head and the bone screw are manufactured separately, and have a rotating/revolving feature that allows free relative rotation between the retaining head and the bone screw.
The known spine fixation device has a pressure element arranged inside the retaining head for the head of the bone screw and a place for insertion of the rod. The pressure element pushes the head of the bone screw against a head part as is known in the art to hold and prevent rotation of the bone screw (for example, see Japanese Patent Application No. 2011-206538). However, this construction puts the bone screw in a condition where it is temporarily fixated within the retaining head. For example, during surgery to fix a deformed spine of a scoliosis patient, when there is a heavy load against the retaining head and the bone screw, the relative angle between the retaining head and the bone screw can change. To prevent changing of the angle, a ring can be included that exerts pressure on the bone screw head due to the pressure element within the holder part, thereby fixing the relative angle between the bone screw and the retaining head.
In the above known spine fixation device, the ring that improves the push pressure on the head of the bone screw is manufactured separately from a set screw responsible for fixing the rod. Because of this, the number of parts of the spine fixation device increases, which complicates the configuration of the spine fixation device and also causes an increase in size. Furthermore, the ring and the set screw each require an exclusive tool to fasten each part. As a result, there is an increase in cost to have the appropriate equipment.
The present invention is designed with these problems in mind, so that the object of the present invention is to supply a spine fixation device and a spine fixation system that can readily fix a bone screw and a retaining head.